The human gut harbors approximately one thousand different bacterial species (intestinal microbiota). Intestinal microbiota number 100 trillion cells; over 90 percent of the cells in the body are bacteria. The composition of each person’s microbiome — the body’s bacterial make-up — is very different, due to the types of bacteria people ingest in their early lives, as well as the effects of diet and lifestyle.
Several studies implicated intestinal bacteria in various cancers. Gram-negative Helicobacter species were found to be associated with liver cancer, colon cancer, and breast cancer. A recent study published in the peer reviewed journal Nature by Yoshimoto et al. (2013) reported that gut bacteria of obese mice unleash high levels of an acid that promotes liver cancer. In rodents, intestinal bacteria influence obesity, intestinal inflammation and certain types of epithelial cancers. However, in human, little is known about the identity of the bacterial species that promote the growth or protect the body from cancer. Therefore, studies are warranted to determine whether differences in peoples’ microbiomes affect their risk for cancer, and whether changing the bacteria can reduce this risk. A clinical trial at the National Cancer Institute (NCI) is currently evaluating the relationship between intestinal bacteria and breast cancer risk (Clinical Trials.gov number: NCT01461070).
For the first time, a recent study by Yamamoto et al. (2013) demonstrated a relationship between intestinal microbiota and onset of lymphoma (a type of blood cancer of B or T lymphocytes). Yamamoto and colleagues studied mice with ataxia-telangiectasia (A-T), a genetic disease that in humans and mice is associated with a high rate of B-cell lymphoma. These investigators discovered that of mice with A-T, those with certain microbial species lived much longer than those with other bacteria before developing lymphoma, and had less of the gene damage (genotoxicity) that causes lymphoma. A high-throughput sequence analysis of rRNA genes identified the bacteria Lactobacillus johnsonnii in abundance in more cancer-resistant mouse colonies compared to cancer-prone mouse colonies.This study by Yamamoto et al. also created a detailed catalog of bacteria types with promoting or protective effects on genotoxicity (a chemical or other agent that damages cellular DNA, resulting in mutations or cancer) and lymphoma, which could be used in the future to formulate combination therapies that kill the bacteria that promote cancer (such as antibiotics) and increase the presence of the bacteria that protect from cancer (like probiotics).
1. Ward, J.M., et al., Chronic active hepatitis in mice caused by Helicobacter hepaticus. Am J Pathol, 1994. 145(4): p. 959-68.
2. Yoshimoto, S., et al., Obesity-induced gut microbial metabolite promotes liver cancer through senescence secretome. Nature, 2013. 499(7456): p. 97-101.
3. Yamamoto, M.L., et al., Intestinal Bacteria Modify Lymphoma Incidence and Latency by Affecting Systemic Inflammatory State, Oxidative Stress, and Leukocyte Genotoxicity. Cancer Res, 2013. 73(14): p. 4222-4232.